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EX4650 Network Cable and Transceiver Planning

Pluggable Transceivers Supported on EX4650 Switches

EX4650 switches support SFP, SFP+, and QSFP+ transceivers. You can find the list of transceivers supported on EX4650 switches and information about those transceivers at the Hardware Compatibility Tool page for EX4650.

Note:

We recommend that you use only optical transceivers and optical connectors purchased from Juniper Networks with your Juniper Networks device.

CAUTION:

If you face a problem running a Juniper Networks device that uses a third-party optic or cable, the Juniper Networks Technical Assistance Center (JTAC) can help you diagnose the source of the problem. Your JTAC engineer might recommend that you check the third-party optic or cable and potentially replace it with an equivalent Juniper Networks optic or cable that is qualified for the device.

The Gigabit Ethernet SFP+, and QSFP+ transceivers installed in EX4650 switches support digital optical monitoring (DOM): You can view the diagnostic details for these transceivers by issuing the operational mode CLI command show interfaces diagnostics optics.

Note:

The transceivers support DOM even if they are installed in the SFP+ uplink module ports.

SFP28 Direct Attach Copper Cables for EX4650 Switches

Small form-factor pluggable transceiver (SFP28) direct attach copper (DAC) cables, also known as Twinax cables, are suitable for in-rack connections between servers and switches. They are suitable for short distances, making them ideal for highly cost-effective networking connectivity within a rack and between adjacent racks.

Note:

We recommend that you use only SFP28 DAC cables purchased from Juniper Networks with your Juniper Networks device.

CAUTION:

If you face a problem running a Juniper Networks device that uses a third-party optic or cable, the Juniper Networks Technical Assistance Center (JTAC) can help you diagnose the source of the problem. Your JTAC engineer might recommend that you check the third-party optic or cable and potentially replace it with an equivalent Juniper Networks optic or cable that is qualified for the device.

Cable Specifications

EX4650 switches support SFP28 passive DAC cables. The passive Twinax cable is a straight cable with no active electronic components. EX4650 switches support 1  m, 3  m, and 5  m long SFP28 passive DAC cables. See Figure 1.

Figure 1: SFP28 Direct Attach Copper Cables for EX4650 SwitchesSFP28 Direct Attach Copper Cables for EX4650 Switches

The cables are hot-removable and hot-insertable: You can remove and replace them without powering off the switch or disrupting switch functions. A cable comprises a low-voltage cable assembly that connects directly into two 25-Gigabit Ethernet ports, one at each end of the cable. The cables use high-performance integrated duplex serial data links for bidirectional communication and are designed for data rates of up to 25  Gbps.

Standards Supported by These Cables

The cables comply with the following standards:

QSFP28 Direct Attach Copper Cables for EX4650 Switches

Quad small form-factor pluggable (QSFP28) direct attach copper (DAC) cables are suitable for in-rack connections between QSFP28 ports on EX4650 switches. They are suitable for short distances, making them ideal for highly cost-effective networking connectivity within a rack and between adjacent racks.

Note:

We recommend that you use only QSFP28 DAC cables purchased from Juniper Networks with your Juniper Networks device.

CAUTION:

If you face a problem running a Juniper Networks device that uses a third-party optic or cable, the Juniper Networks Technical Assistance Center (JTAC) can help you diagnose the source of the problem. Your JTAC engineer might recommend that you check the third-party optic or cable and potentially replace it with an equivalent Juniper Networks optic or cable that is qualified for the device.

Cable Specifications

QSFP28 passive DAC cables are hot-removable and hot-insertable. A cable consists of a cable assembly that connects directly into two QSFP28 modules, one at each end of the cable. The cables use integrated duplex serial data links for bidirectional communication and are designed for data rates up to 100 Gbps. Passive DAC cables have no signal amplification built into the cable assembly. See Figure 2.

Figure 2: QSFP28 Direct Attach Copper CablesQSFP28 Direct Attach Copper Cables

Calculating the Fiber-Optic Cable Power Budget for EX Series Devices

To ensure that fiber-optic connections have sufficient power for correct operation, calculate the link's power budget when planning fiber-optic cable layout and distances to ensure that fiber-optic connections have sufficient power for correct operation. The power budget is the maximum amount of power the link can transmit. When you calculate the power budget, you use a worst-case analysis to provide a margin of error, even though all the parts of an actual system do not operate at the worst-case levels.

To calculate the worst-case estimate for fiber-optic cable power budget (PB) for the link:

  1. Determine values for the link's minimum transmitter power (PT) and minimum receiver sensitivity (PR). For example, here, (PT) and (PR ) are measured in decibels, and decibels are referred to one milliwatt (dBm).

    PT = – 15 dBm

    PR = – 28 dBm

    Note:

    See the specifications for your transmitter and receiver to find the minimum transmitter power and minimum receiver sensitivity.

  2. Calculate the power budget (PB) by subtracting (PR) from (PT):

    – 15 dBm – (–28 dBm) = 13 dBm

Calculating the Fiber-Optic Cable Power Margin for EX Series Devices

Before calculating the power margin:

Calculate the link's power margin when planning fiber-optic cable layout and distances to ensure that fiber-optic connections have sufficient signal power to overcome system losses and still satisfy the minimum input requirements of the receiver for the required performance level. The power margin (PM) is the amount of power available after attenuation or link loss (LL) has been subtracted from the power budget (PB).

When you calculate the power margin, you use a worst-case analysis to provide a margin of error, even though all the parts of an actual system do not operate at worst-case levels. A power margin (PM ) greater than zero indicates that the power budget is sufficient to operate the receiver and that it does not exceed the maximum receiver input power. This means the link will work. A (PM) that is zero or negative indicates insufficient power to operate the receiver. See the specification for your receiver to find the maximum receiver input power.

To calculate the worst-case estimate for the power margin (PM) for the link:

  1. Determine the maximum value for link loss (LL) by adding estimated values for applicable link-loss factors—for example, use the sample values for various factors as provided in Table 1 (here, the link is 2 km long and multimode, and the (PB) is 13 dBm):
    Table 1: Estimated Values for Factors Causing Link Loss

    Link-Loss Factor

    Estimated Link-Loss Value

    Sample (LL) Calculation Values

    Higher-order mode losses (HOL)

    • Multimode—0.5 dBm

    • Single mode—None

    • 0.5 dBm

    • 0 dBm

    Modal and chromatic dispersion

    • Multimode—None, if product of bandwidth and distance is less than 500 MHz/km

    • Single mode—None

    • 0 dBm

    • 0 dBm

    Connector

    0.5 dBm

    This example assumes 5 connectors. Loss for 5 connectors:

    (5) * (0.5 dBm) = 2.5 dBm

    Splice

    0.5 dBm

    This example assumes 2 splices. Loss for two splices:

    (2) * (0.5 dBm) = 1 dBm

    Fiber attenuation

    • Multimode—1 dBm/km

    • Single mode—0.5 dBm/km

    This example assumes the link is 2  km long. Fiber attenuation for 2 km:

    • (2 km) * (1.0 dBm/km) = 2 dBm

    • (2 km) * (0.5 dBm/km) = 1 dBm

    Clock Recovery Module (CRM)

    1 dBm

    1 dBm

    Note:

    For information about the actual amount of signal loss caused by equipment and other factors, see your vendor documentation for that equipment.

  2. Calculate the (PM) by subtracting (LL) from (PB):

    PB – LL = PM

    (13 dBm) – (0.5 dBm [HOL]) – ((5) * (0.5 dBm)) – ((2) * (0.5 dBm)) – ((2 km) * (1.0 dBm/km)) – (1 dB [CRM]) = PM

    13 dBm – 0.5 dBm – 2.5 dBm – 1 dBm – 2 dBm – 1 dBm = PM

    PM = 6 dBm

    The calculated power margin is greater than zero, indicating that the link has sufficient power for transmission. Also, the power margin value does not exceed the maximum receiver input power. Refer to the specification for your receiver to find the maximum receiver input power.